The idea that a mugshot should be universally unsmiling is a social norm, it’s not a law and I wouldn’t see it like some kind of rule. My psych ward mugshot from the beginning of my dark times is still visible to anyone who looks me up by name, and I am quite thankful I was smiling in it, even if the only reason I was smiling was to try to imply nothing was wrong with me. Smiling is also a form of acknowledgement.